Recently, radio frequency identification tags (hereinafter, may be referred to simply as “RFID tag”) and systems using such tags have been intensively studied and developed. The RFID tag has been expected to be used in various systems. For example, the application of such a tag to a security system that carries out an authentication process for people to come in or go out has been proposed. In this case, the authentication process is carried out by confirming the presence or absence of the RFID tag through radio data transmission.
Since the RFID tag of this type requires an antenna element, there have been demands for a technique for forming an antenna element in various substrates. For example, WO 99/67754 and WO 00/16286 have disclosed devices using the RFID tag of this type and methods relating to the devices, in which an antenna element is formed on a substrate. For example, WO 99/67754 discloses a method in which a conductor is joined to a substrate to form an antenna element. Moreover, WO 00/16286 discloses a method in which a conductor is formed on a substrate to form an antenna element, with the adhesion between the antenna element and the substrate being enhanced by using an adhesive and the like.
However, the conductors (antenna element) formed on substrates, disclosed in WO 99/67754 and WO 00/16286, have an inferior bending property. Thus, the conductors have some problems such that the conductor is disconnected, when the conductive portion is bent by 180 degrees, or when the bending process is repeated several times.
With respect to a conductor material having a good bending property, for example, conductive polymers and shape-memory alloys are proposed. For example, WO 01/59880A1 has disclosed a conductive polymer. It has been proposed that an antenna element is formed by using such a conductive polymer as a conductive material. Moreover, Japanese Patent Application Laid-Open (JP-A) No. 7-147508 has disclosed a shape-memory alloy and proposed that an antenna element can be formed by using the shape-memory alloy as the conductive material in a manner similar to the conductive polymer. However, even if the conductive polymer or the shape-memory alloy having a bending property is used, it is not possible to obtain sufficient durability to bending by 180 degrees, at present. Moreover, the shape-memory alloys used also have a problem of high costs.